Kasprzak denied attempted murder but was found guilty by a jury at Leeds Crown Court today after three days of deliberation.

Kasprzak, a meat factory worker, of Penistone Road, Huddersfield, told the court he only meant to scare Miss Lewandowska and did not intend to kill her.

Co-defendant Patryk Borys, 18, of Rashcliffe Hill Road, Huddersfield, who did not give evidence, was cleared of the same charge.

Both men admitted kidnap at a previous hearing, while Kasprzak also admitted possessing a prohibited weapon.

In a statement read outside court after the verdict, Miss Lewandowska described how she feared she would die inside the box and still has nightmares about her ordeal.

She said the thought of her young son gave her the strength to save herself.

"During my time inside my shallow grave where I was buried alive, I feared that my life was at an end and I was going to die," she said.

"I prayed to God to help me to survive so that I could look after my young son. The thought of my son gave me the strength to fight my way out of the box and save myself.

"For many years I loved Marcin Kasprzak very much. But after his horrific attack upon me my feelings towards him have turned to hatred.

"I still have nightmares that Marcin will come back to find me and kill me. My only hope is that he can accept that what he did to me was very wrong.

"I really hope that no one will ever experience what I went through on that day in May, at the hands of a man whom I loved and trusted."

Detective Chief Inspector Lisa Griffin, of West Yorkshire Police's homicide and major inquiry team, commended Miss Lewandowska for her bravery and described Kasprzak as "an intimidator of vulnerable women".

She said it had been proved the crime was not a "prank" but "a serious and determined attempt to end a young mother's life".

The court heard that the Polish couple's relationship had broken down at the time of the attack, and that he "hated" her and feared she wanted to take Jakub back to home to Poland and never return to the UK.

Jurors were told that Miss Lewandowska, a mender at a clothing factory, spent 30 minutes buried in the box before escaping.

Meanwhile, her former fiancé took her bank card and withdrew £500 before returning to his accomplice's home, where they were arrested about nine hours later. He later told police that he had intended to free her but forgot after falling asleep.

Jonathan Sharp, prosecuting, had told the jury that the case was about a young man who had become "bored" with his partner, and had "decided to get rid of her".

Det Chief Insp Griffin added: "The victim in this terrifying ordeal demonstrated tremendous bravery and undoubtedly saved her own life by freeing herself from the box that Kasprzak had buried her in.

"Now that Kasprzak has been found guilty for attempting to murder her, I hope that this brave woman will be able to move on with her life.

"Kasprzak has shown himself to have been an unpleasant intimidator of vulnerable woman and I am pleased that he is now behind bars where he belongs.

"I would like to close by thanking the motorist who went to the victim's aid by stopping for her and helping her to raise the alarm."

Peter Collier QC, the Recorder of Leeds, adjourned sentencing until January 13, warning the pair: "Clearly a custodial sentence will follow."